1. Field of the Invention
The present invention relates to artificial limbs and, more particularly, to a durable, prosthetic foot and ankle joint which is capable of movement in multiple directions during use, so as to simulate movement of a natural human ankle.
2. The Prior Art
When possible, most foot and leg amputees wear prostheses in order to provide them with greater mobility and to permit them to participate in more activities. In order to perform most effectively and to fulfill its intended purpose, a prosthesis should be comfortable to wear and should simulate the natural movements of the limb and joints it replaces.
A foot prosthesis is generally shaped like a foot so as to fit within ordinary shoes. The prosthesis is generally anchored to the leg of the wearer by a socket member which fits over the stump of the leg. Depending upon the position of the amputation, the prosthesis may include a section which represents a portion of the leg to which the artificial foot is connected.
At the present time, the most common type of foot prosthesis is the SACH (solid ankle, cushioned heel) foot. Because it does not include any movable parts, the SACH foot is the simplest and least expensive prosthesis to build. However, the SACH foot has several drawbacks. For example, inasmuch as the ankle is not jointed, the foot is not capable of any type of rotational or bending movement. Accordingly, a person wearing this type of foot usually walks with a limp.
Additionally, as a person walks and turns during normal use of limbs such as the SACH foot, the socket which secures the prosthesis to the person's leg can rub against the stump. Depending upon the quality of fit between the prosthesis and the stump, this rubbing can cause sores to develop on the stump. These sores can become so severe that a person must remove the prosthesis for extended periods to allow them to heal. Because of the discomfort often experienced with these types of limbs, as well as their inability to provide for rotational or bending movement, many amputees are dissatisfied with the limbs and are seeking something better.
In an effort to eliminate some of the irritation which occurs to the stump of an amputee and to provide greater movement of the foot so that the amputee can participate in a wider range of activities, various attempts have been made to develop movable ankle joints. One such joint provides a single axis of rotation which allows the foot to bend forward and back at the ankle. By providing a single axis of rotation, some of the irritation which occurs during normal walking can be reduced, thereby providing a more natural movement which helps eliminate any limp.
Another modification which has been made to achieve greater flexibility is the inclusion of a device commonly referred to as a rotator. This device is positioned between the foot and the leg of the prosthesis, at the ankle joint. The rotator provides a slight amount of angular rotation about the axis of the ankle so that a person, while having his foot planted, can turn slightly in one direction or another without having to lift or drag the foot. The rotator also facilitates turning while a person is walking.
However, the prior art rotator devices have several drawbacks. First, the inclusion of a rotator in the artificial limb significantly increases the cost of a prosthesis. Second, rotators are relatively heavy, and thus they increase the overall weight of the prosthesis and make it more difficult to walk. Third, rotators, by themselves, only allow rotational movements about the ankle and not other types of desireable movements such as those required for the foot to move forward and back during walking. Hence, still more devices must be included in the prosthesis to allow for such other types of movements.
In light of the foregoing, it is clear that while the inclusion of single axis joints and rotators can increase the flexibility of a foot prosthesis, they still fall far short of adequately simulating the natural movements of an ankle joint.
In an attempt to more closely approximate the features of a normal ankle, an ankle joint was developed which utilized a ball and socket to provide movement of the foot prosthesis in more directions. Such a joint is disclosed in U.S. Pat. No. 2,643,391, issued to Roderick W. McKendrick. This ball and socket joint allows both bending movement as the person walks and also a slight amount of rotational movement. While this joint has solved some of the problems in the prior art, other drawbacks to the use of this joint remain.
For example, the parts of the McKendrick joint have a tendency to wear upon each other as a person uses the joint in walking, thus necessitating frequent repair or replacement of the parts. Additionally, it is common for these joints to develop annoying squeaks as a person walks. It readily becomes clear to a user of this device that, as with the other foot and ankle prostheses presently available, the device often does not provide the full range of desirable capabilities necessary to permit the user to enjoy the desired lifestyle.
Accordingly, what is needed in the art is a foot and ankle joint which is light in weight and which allows movements of the foot in multiple directions, similar to those movements available to a normal foot, while also being sufficiently sturdy to perform under normal use without breakage, excessive wear, or other undesirable side effects such as squeaking. Such a device is disclosed and claimed herein.